netdev - Re: changing dev->needed_headroom/needed

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Message-ID: <1375433758.24371.20.camel@deadeye.wl.decadent.org.uk>
Date:	Fri, 2 Aug 2013 10:55:58 +0200
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Johannes Berg <johannes@...solutions.net>
CC:	<netdev@...r.kernel.org>, <linux-wireless@...r.kernel.org>
Subject: Re: changing dev->needed_headroom/needed_tailroom?

On Fri, 2013-07-26 at 16:50 +0200, Johannes Berg wrote:
> Does it seem reasonable to change dev->needed_headroom and
> dev->needed_tailroom on the fly?
> 
> We currently set needed_headroom to the max of what we need, but we
> could do better like making it depend on the interface type (e.g. only
> asking for mesh space on mesh interfaces). This would be done only when
> the interface isn't connected, I can't promise it would be down but the
> carrier would be off.
[...]

I don't think this is safe when the interface is running (even if
carrier is off).  Some functions may read dev->needed_headroom twice and
rely on getting the same value each time.

Also, stacked devices would need to adjust their own needed_headroom
accordingly.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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